A rotational angle detecting device is used for shift position detection of an automatic transmission and depression angle detection of an accelerator pedal or a brake pedal for a vehicle, and in recent years a magnetic type thereof adapted for severe in-vehicle environments such as vibrations, temperature changes and dusts has been increasingly in demand.
For example, Japanese Patent No. 5131537 discloses a conventional rotational angle detecting device of a magnetic type configured of a rotational member on the periphery of a rotational center of which permanent magnets are arranged to alternate an N pole region thereof with an S pole region thereof, and a plate-shaped magnetic plate and magnetic detection elements arranged in a predetermined position to the rotational member, wherein a rotational angle of the rotational member is calculated based upon the detection result of magnetic field components in two directions in the magnetic plate.
However, according to the conventional rotational angle detecting device, when the rotational member equipped with the permanent magnets is included in the angle sensor unit positioned to face the detected object, because of rotating the rotational member in association with the detected object, a rotation transmitting mechanism for transmitting the rotation of the detected object becomes necessary. Therefore constraint conditions on the detected object and its installation portion are increased and further, high detection precision cannot be obtained because of mechanical errors in the rotation transmitting mechanism.
Further, the angle sensor unit accommodated in a case and formed as a one-piece product is internally required to air-tightly form a space accommodating the rotational member and hold the rotational member with good positional accuracy. Therefore the angle sensor unit is difficult to be miniaturized and its complicated holding structure causes an increase in manufacturing costs.
In addition, even if the rotational member and the detected object are formed as a one-piece combined body by making the detected object penetrate through an axis center of the rotational member for making the rotation transmitting mechanism unnecessary, precision work for its combination causes an increase in costs and it is difficult to perform an appropriate seal on the angle sensor unit side.
Further, even if the permanent magnet is attached to the detected object by eliminating the rotational member, it complicates the manufacturing process for forming a mounting structure thereof on the detected object and requires a strict management on magnetic contamination due to attachment of small pieces and micronized powder of magnetic substances containing metallic materials in the manufacturing process.
In addition, when eccentricity of a rotational axis of the detected object occurs, a rotational axis of the permanent magnet is also shifted in position to change a relative positional relation to a magnetic detection element, thus creating variations in output signals.
Therefore even if any of the above-mentioned measures is adopted, it is difficult to accomplish both the detection precision and the low manufacturing cost in the structure of rotating the permanent magnet in association with the detected object.